Journal of Neuroscience, Vol 11, 2460-2476, Copyright © 1991 by Society for Neuroscience
A unique neuronal organization in the cat pretectum revealed by antibodies to the calcium-binding protein calbindin-D 28K
LB Nabors and RR Mize
Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis 38163.
The pretectum is an important center for visual reflexes. However, the
location, boundaries, and connections of individual nuclei of the pretectum
are incompletely understood. In cat, the traditionally defined nuclear
boundaries have been placed in doubt by recent evidence showing that the
retinal input to the pretectum forms four continuous projection zones that
do not match the cytoarchitectural boundaries of individual pretectal
nuclei defined by previous studies. We now show that antibodies to the
calcium-binding protein calbindin-D 28K (CaBP) label clusters of neurons
within the pretectum that match the zones of retinal termination. Four
obvious cell clusters within the pretectum were labeled by CaBP antisera.
Computer three-dimensional reconstruction of these cell clusters revealed
that they form four distinct but continuous zones that run the rostrocaudal
length of the pretectum in a medial-to-lateral direction. By combining
anterograde HRP labeling of retinal terminals with CaBP
immunocytochemistry, these CaBP-labeled cell clusters were found virtually
to overlap the retinal projection zones. The CaBP-labeled neurons included
both multipolar and fusiform morphologies, and most were medium- to
large-sized cells. HRP retrograde transport studies showed that many
CaBP-labeled neurons in the clusters projected to the LGN, while none
projected to the inferior olive (IO). GABA-immunoreactive neurons were also
found within the CaBP cell clusters, but these neurons were smaller than
most CaBP-labeled neurons, and none were retrogradely labeled following HRP
injections into the LGN or IO. Two-color antibody double-labeling
experiments did not reveal any GABA neurons within the clusters that
colocalized CaBP. In summary, calbindin is a precise marker of neuron
clusters that overlap the retinal projection zones in the cat pretectum.
Many of these CaBP neurons project to the LGN, and none contain GABA.